Heat transfer processes, electrophotographic processes, ink jet processes, etc., have been vigorously investigated as a technique for forming color hard copy. A heat transfer process has many advantages as compared to other processes since in a heat transfer process, the apparatus can be easily maintained and operated. The apparatus and the supplies therefor are inexpensive.
Such systems include a system of heating a heat transfer material composed of a base film having formed thereon a heat melting ink layer, by a thermal head to melt the ink and to record on a heat transfer image-receiving layer. Also known is a system of heating a heat transfer dye providing material composed of a base film having formed thereon a dye-providing layer containing a heat migrating dye, by a thermal head to heat migrating transfer the dye onto a heat transfer image-receiving material.
Since in the latter heat migrating transfer system, the transferring amount of dye can be changed by changing the energy applied to the thermal head, a gradation record (continuous tone record) can be easily obtained and hence the latter system is particularly useful for full color recordings of high image quality.
However, there are various restrictions on the heat migrating dye being used in this system. Dyes meeting all the properties required are very few.
The properties required for the heat migrating dye include that (i) the dye has preferably suitable spectral characteristics for color reproduction, (ii) the dye can easily cause heat migrating, (iii) the dye has a strong resistance to light and heat, (iv) the dye has a strong resistance to various chemicals, (v) the dye does not readily reduce the sharpness, (vi) the images of the dye formed do not readily retransfer, (vii) the dye does not cause bleeding out, crystallization, or aggregation in an image-receiving material for a long period of time, (viii) a heat transfer dye providing material can be easily prepared using the dye, (ix) the dye does not cause crystallization or aggregation in the heat transfer dye providing material for a long period of time, etc.
Dyes which satisfy all the requirements are not known at present, but the pyrazoloazole series azomethine dyes described in JP-A-64-63194 have very good properties as a magenta dye.
However, even the foregoing dyes do not satisfy all the properties described above. As the result of various investigations, the inventors have learned about the substituents of the coupler moieties of a pyrazoloazole series azomethine dye and the properties of the heat migrating dye and have succeeded in accomplishing the present invention.
Pyrazoloazole series azomethine dyes, the coupler moieties of which are substituted with an aryl group or a heterocyclic group, are excellent in fastness and heat migrating property. But in many of these dyes, the absorption wave form is broader than that of a pyrazoloazole series azomethine dye, the coupler moiety of which is substituted by an alkyl group.
The inventors believe that if the broadness of the absorption wave form of the foregoing dye is corrected, the dye becomes an excellent heat migrating dye. Thus, the inventors have investigated the substituents of the aryl group and the heterocyclic group of the coupler moiety and the properties of the heat migrating dye.
It is known in the field of a silver salt photography that when in a pyrazoloazole series coupler substituted by an aryl group, the ortho-position of the bonded position of the aryl group is substituted by an alkoxy group, etc., the absorption of the dye formed by the reaction of the coupler with a color developing agent becomes sharper than that of a dye originating from a coupler having no substituent at the orthoposition.
However, it was believed that the foregoing fact could not be applied to a heat migrating dye. First, it was anticipated that by newly introducing a substituent, the molecular weight was increased to reduce the heat migrating property. Second, if a substituent having a high electrical negativity, such as a halogen atom, a hetero atom, etc., is newly introduced, there were apprehesions that the electrostatic interaction between dyes would become large and cause the aggregation, deposition, and crystallization of the dyes in the dye-providing material and the image-receiving layer after heat transfer of the dyes. Third, it was expected that by the introduction of a new substituent, the interaction between the binder molecule and the dye in the dye-providing material and the image-receiving layer would be increased, resulting in an increase of the heat migrating property of the dye in the dye providing material.
As the result of various investigations, the inventors have found that contrary to the foregoing expectations, in the dyes in which the substituent of the coupler moiety is an aryl group or a heterocyclic group, the pyrazoloazole series azomethine dyes having the substituent at the ortho-position of the bonded position are excellent in their heat migrating property and solubility of the dyes in a solvent at the time of preparation of an ink, as compared with the dyes having no substituent at the ortho-position.
Furthermore, it has been found that a dye having a substituent at the ortho-position does not readily cause aggregation, deposition, crystallization, bleed out, etc., for a long period of time in the dye providing material or the image-receiving layer after transfer as, compared to the dyes having no substituent at the ortho-position. In addition, in the case of the dye having the substituent at the ortho-position, the occurrence of retransfer of dye images and blurring of dye images are reduced. These discoveries are utterly unexpected.
By these unexpected discoveries, it has become possible to invent pyrazoloazole series azomethine dyes substituted by an aryl group or a heterocyclic group at the ortho-position having a sharpened absorption waveform without reducing the properties required for a heat migrating dye.
European Patent 284,239 and JP-A-63-231341 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") describe pyrazoloazole couplers being used for silver halide color photographic materials. That is, the dye formed from a pyrazoloazole coupler wherein one carbon atom directly bonded to the pyrazoloazole nucleus is included in an aryl group or a heterocyclic group and the coupler has an alkyl group, an alkoxy group or a halogen atom at at least one ortho-position of the carbon atom migrates the absorption maximum to a short wave side, reduces the half value width, and increases the light-fastness.
However, the present invention is not restricted by the foregoing disclosure of the patents.
A photographic coupler is a compound which is fixed in an oil droplet in a form which is hard to diffuse and becomes a dye by reacting with a color developing agent. Also, the structure of a coupler is designed so that the coupler and a dye formed from the coupler do not diffuse from the photographic layer in each step of development, bleach, fix, or wash.
Accordingly, it is impossible to anticipate the heat migrating property of the dye in the present invention from the foregoing disclosures of the patents about the coupler, the diffusion of which is prevented.
Furthermore, the foregoing couplers have a ballast group (non-diffusible group). The ballast group also functions as an oil-solubilizing group, whereby the couplers can dissolve well in oil droplets. That is, the solubility of the compound formed by removing the ballast group from the foregoing coupler compound is unknown and hence it can not be anticipated from the disclosures of the foregoing patents what the states of aggregation, crystallization, and deposition, and the ink aptitude of the compounds of the present invention would be in the dye providing material and the image-receiving layer. Moreover, JP-A-64-48863 describes a pyrazolotriazole series azomethine dye wherein the substituent of the coupler moiety is an ortho-acylaminophenyl group or an ortho-sulfonylaminophenyl group.
However, the present invention is not restricted by the dye described in the foregoing patent application.
Specifically, there is no description in the foregoing patent application of the heat migrating property, the solubility, the crystallinity, etc., of the foregoing dye. Further, there is no description of the change of the absorption based on the type of the substituent at the ortho-position of the aryl group.
Furthermore, the dyes described in the foregoing patent application are cyan dyes, which have no relation with the compounds of the present invention, which are used mainly as magenta dyes.
In other words, it is impossible to anticipate the heat migrating property and occurrence of the aggregation of the compounds in the materials of the present invention from the descriptions of the above-described patent application.